A method of surface heat treatment of an austenitic stainless steel weld

Abstract

The application discloses an austenitic stainless steel weld surface layer heat treatment method, a heating area is arranged on the weld surface layer, cooling areas are arranged on both sides of the heating area, a temperature measuring area is arranged on the back of the weld corresponding to the heating area, and the method comprises the following steps: (1) determining the heat treatment process parameters of the heating area; (2) determining the position of the cooling area and the temperature of the temperature measuring area through numerical simulation; (3) arranging a heating device, a cooling device and a temperature measuring device; (4) implementing heat treatment on the heat treatment object according to the set heat treatment process parameters; and (5) removing the heating device, the cooling device and the temperature measuring device after the heat treatment is completed. The application combines the induction heating device and the cooling device, improves the mechanical properties and microstructure of the weld surface layer by means of solid solution treatment, makes the carbide in the as-cast structure of the stainless steel weld dissolve in the matrix, reduces the residence time of the base material in the sensitization temperature zone, avoids the deterioration caused by Cr 23 precipitation.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology, and specifically to a surface heat treatment method for austenitic stainless steel welds. Background Technology

[0002] In practical engineering, post-weld stress-relieving heat treatment of stainless steel containers and equipment is often controlled at 600–650℃ to eliminate residual post-weld stress, improve the as-cast microstructure of the weld, and control deformation. However, this temperature range coincides with the sensitization range of austenitic stainless steel, and prolonged exposure at this temperature can easily cause Cr… 23 Carbides such as C6 precipitate between austenitic grains. Therefore, post-weld heat treatment of austenitic stainless steel can only be carried out in a higher temperature range, and water cooling should be used to cool it down as soon as possible to cross the sensitization range.

[0003] However, higher temperatures pose more severe challenges to the stress and deformation of stainless steel containers. High-frequency electromagnetic induction heating is used in the heat treatment of containers due to its fast heating speed, high temperature, and low cost; at the same time, its controllability of the heated parts makes local solution treatment of austenitic stainless steel welds possible. However, conventional induction heating has certain problems due to its process conditions and tooling: (1) laying the insulation layer is time-consuming and labor-intensive; (2) the long holding time during heating makes the temperature too high in the entire weld depth direction, while most austenitic stainless steel components only require good performance on a single surface in contact with the corrosive medium; (3) there may be a phenomenon where the temperature range of the material at a certain distance from the direct heating area of ​​the induction cable coincides with the sensitization temperature, and the presence of the insulation layer causes this part of the structure to remain at the sensitization temperature for a long time; (4) the insulation layer must be removed before water cooling after heating, and the resulting untimely cooling may cause the carbides dissolved in the matrix to re-precipitate. Based on this, the present invention proposes a surface heat treatment method for austenitic stainless steel welds. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a surface heat treatment method for austenitic stainless steel welds. By combining an induction heating device and a cooling device, solution treatment is used to improve the surface mechanical properties and microstructure of the weld, thereby enhancing the corrosion resistance of the weld surface and reducing the deformation and temperature control difficulties of conventional overall heat treatment.

[0005] The technical solution adopted in this invention is as follows:

[0006] A surface heat treatment method for austenitic stainless steel welds includes setting a heating zone on the weld surface, setting cooling zones on both sides of the heating zone, and setting a temperature measuring zone on the back of the weld corresponding to the heating zone, comprising the following steps:

[0007] (1) Determine the heat treatment process parameters of the heating zone

[0008] The heat treatment process parameters of the heating zone are determined based on the material properties and weld size of the object to be heat treated, including the heat treatment termination temperature, the width of the heating zone, and the induction heating method.

[0009] (2) Determine the location of the cooling zone and the temperature of the temperature measurement zone through numerical simulation.

[0010] Based on the material properties, material structure parameters and heat treatment process parameters of the heat-treated object in step (1), an induction heating numerical simulation test is performed on the heat-treated object to obtain the time-temperature curve along the axial direction of the weld surface and the time-temperature curve of the back temperature measurement area of ​​the weld. The location of the cooling zone is determined based on the time-temperature curve of the weld surface. The temperature value of the back of the weld when the temperature of the weld surface reaches the heat treatment termination temperature in step (1) is determined based on the time-temperature curve of the heating zone of the weld surface and the time-temperature curve of the back temperature measurement area of ​​the weld. This temperature value is used as the heating termination temperature.

[0011] (3) Arrange heating devices, cooling devices and temperature measuring devices.

[0012] (31) An electromagnetic induction heating device is arranged on the surface of the weld of the heat-treated object according to the width of the heating zone determined in step (1); the electromagnetic induction heating device maintains a certain gap with the surface of the weld of the heat-treated object through a vertically placed iron sheet or heat-resistant plate, the gap being 5 to 10 mm, and the electromagnetic induction heating device is as close as possible to the weld heating zone.

[0013] (32) According to the location of the cooling zone determined in step (2), a set of cooling devices are arranged in the cooling zones on both sides of the heating zone. Each set of cooling devices consists of three perforated copper pipes, with water as the cooling medium in the middle perforated copper pipe and air as the cooling medium in the other two perforated copper pipes.

[0014] (33) Arrange thermocouples or infrared thermometers in the temperature measurement area on the back of the weld of the heat-treated object as temperature measurement devices, and obtain the time-temperature curve of the temperature measurement area on the back of the weld.

[0015] (4) Heat treatment implementation

[0016] The electromagnetic induction heating device heats the surface of the weld of the heat treatment object with a constant power. The heating stops when the temperature of the temperature measuring area on the back of the weld reaches the heating termination temperature determined in step (2). During the heating process, the open copper pipe with air as the cooling medium is opened intermittently. After the heating stops, the induction heating power is turned off, and the open copper pipe with water as the cooling medium or both water and air as the cooling medium is turned on to cool down. After the temperature of the temperature measuring area on the back of the weld reaches room temperature as measured by the temperature measuring device, the corresponding open copper pipe is turned off. In addition, if the surface temperature of the weld of the heat treatment object cannot be rapidly increased to the set heat treatment temperature at 600-700℃ / min due to the power or frequency limitation of the induction power, the open copper pipe with air as the cooling medium does not need to be opened intermittently during the heating process. After the heating is completed, the open copper pipe with water as the cooling medium is turned on to cool down.

[0017] (5) Remove the heating device, cooling device and temperature measuring device.

[0018] After the heat treatment is completed, the heating device, temperature measuring device and cooling device are removed, and the weld is subjected to non-destructive testing.

[0019] Furthermore, in step (1), the wall thickness of the heat-treated object is more than 10 mm, the heat treatment termination temperature is 1050-1080℃, and the width of the heating zone is the weld and the weld extends 5-10 mm towards the base material.

[0020] In the above technical solution, the weld thickness of the heat treatment object to which this invention is applicable is preferably 10mm. The weld with a larger thickness has more uneven overall cooling and more serious carbide precipitation. On the other hand, the weld with a thinner thickness has a faster thermal conductivity and has higher requirements for subsequent cooling response. If the weld thickness of the heat treatment object is more than 50mm, the induction heating power supply of the electromagnetic induction heating device needs to be pre-input with a segmented heating rate curve and a termination temperature. In principle, rapid heating is required below 700℃, and the heating rate can be slightly reduced from 700℃ to the heat treatment termination temperature.

[0021] Furthermore, the induction heating in step (1) is high-frequency induction heating.

[0022] Furthermore, the induction heating frequency is 30–100 kHz.

[0023] Furthermore, the specific steps of the numerical simulation experiment in step (2) are as follows:

[0024] Based on the structural dimensions and materials of the heat-treated object, a numerical simulation model is established, and an air domain model with a size 5 to 10 times that of the heat-treated object model is also established.

[0025] The numerical simulation model is meshed, and at least 5 boundary layers are divided in the thickness direction of the heating zone of the heat-treated object during meshing. At the same time, an infinite element domain is set at the edge of the air domain.

[0026] An induction heating device is applied to the numerical simulation model. When modeling the induction heating device numerically, only the coil structure is considered, and the coil is assigned corresponding parameters according to the current and frequency of the induction power supply of the induction heating device.

[0027] Numerical simulation was performed using the finite element method to obtain the time-temperature curves along the axial direction of the weld surface layer and the time-temperature curves of the temperature measurement zone on the back side of the weld.

[0028] In the above technical solution, due to the small distance between the induction heating device and the object being heat-treated during actual heat treatment, the thermocouple arranged at the heating center point on the surface of the object will be affected by the alternating electric field and will not function properly. Furthermore, the shielding of the induction heating device makes the infrared temperature measuring device unusable at the heating center point on the surface of the object. Therefore, a temperature measuring area is set on the back side of the heating zone of the object to reflect the heating effect. To obtain the temperature value of the temperature measuring area on the back side of the weld when the weld surface reaches the set heat treatment termination temperature, a numerical simulation method is used for determination.

[0029] Furthermore, in step (2), when determining the location of the cooling zone based on the time-temperature curve of the weld surface, the area where the temperature on both sides of the weld remains within 600-650℃ for more than one-third of the heating time is selected as the location of the cooling zone.

[0030] Furthermore, in step (2), when determining the heating termination temperature based on the time-temperature curve of the weld surface heating zone and the time-temperature curve of the weld back temperature measurement zone, the temperature of the center point of the weld surface heating zone and the center point of the weld back temperature measurement zone shall be used as the standard.

[0031] Furthermore, in step (31), the electromagnetic induction heating device specifically adopts air-cooled / water-cooled high-temperature resistant cable or copper pipe, and the arrangement width of the electromagnetic induction heating device is equal to the width of the heating zone of the heat treatment object; if the minimum coverage area of ​​the electromagnetic induction heating device parallel to the longitudinal direction of the weld is greater than the width of the heating zone to be heated in the longitudinal direction of the weld of the heat treatment object, so that part of the heating device exceeds the heat treatment object and causes no load, then a magnetic steel plate needs to be placed flat under the part of the no load heating device to prevent power loss caused by leakage magnetism of the electromagnetic reaction heating device.

[0032] Furthermore, in step (32), when arranging the cooling device, the distance between the cooling device and the surface of the heat-treated object is kept at more than 10 mm; and the three perforated copper pipes of the cooling device are all equipped with regulating valves for adjusting the flow rate of the cooling medium.

[0033] Further, in step (33), the temperature measuring device is a thermocouple or an infrared temperature measuring element; when the temperature measuring device is a thermocouple, the thermocouple is fixed to the temperature measuring area on the back of the weld by spot welding, and the thermocouple is preferably a K-type thermocouple; when the temperature measuring device is an infrared temperature measuring element, the infrared temperature measuring element is fixed at a position where the temperature measuring area on the back of the weld can be directly measured, so as to ensure that the temperature measuring point remains stationary during the temperature measurement process.

[0034] In the above technical solution, after the temperature measuring device is installed, it is also necessary to connect the temperature measuring device to the recorder and check and confirm the continuity of the line in order to obtain the corresponding temperature rise curve.

[0035] The beneficial effects of this invention are as follows:

[0036] (1) This invention provides a surface heat treatment method for austenitic stainless steel welds. By combining an induction heating device and a cooling device, solution treatment is used to improve the surface mechanical properties and microstructure of the weld, allowing carbides in the as-cast structure of the stainless steel weld to dissolve into the matrix. Simultaneously, the residence time of the base metal in the sensitization temperature zone is reduced, preventing Cr... 23 The degradation caused by C6 precipitation improves the corrosion resistance of the weld surface;

[0037] (2) This invention provides a surface heat treatment method for austenitic stainless steel welds. By controlling the range of the weld heating zone and the temperature rise of the heating zone, the heat treatment effect of the weld and its surrounding area is guaranteed, while effectively solving the problems of energy consumption and deformation in conventional overall heat treatment. At the same time, the heating area is small and the heat source is concentrated and efficient, avoiding the time-consuming and labor-intensive problem of laying the insulation layer in conventional induction heating heat treatment of engineering components. Attached Figure Description

[0038] To clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a flowchart of the present invention;

[0040] Figure 2 This is a layout diagram of the heating device, cooling device, and temperature measuring device of the present invention;

[0041] Figure 3 The time-temperature curves of the center of the heating zone on the surface of the heating surface are obtained from numerical simulation of induction heating at different frequencies in Embodiment 1 of the present invention.

[0042] Figure 4 The time-temperature curves of the center of the back heating zone of the heating surface in Embodiment 1 of the present invention are obtained by numerical simulation using induction heating at different frequencies.

[0043] Figure 5 The time-temperature curve of the heated surface layer along its axial direction is shown in the numerical simulation of induction heating at a frequency of 30kHz in Embodiment 1 of the present invention.

[0044] Figure 6 The time-temperature curve of the sample surface 70 mm from the center of the heating zone in Example 1 of this invention, which was tested using induction heating at a frequency of 30 kHz.

[0045] Figure 7 This is the time-temperature curve of the center part of the weld surface layer of the plate sample in Comparative Example 1 of the present invention during the heat treatment process. Detailed Implementation

[0046] This invention provides a surface heat treatment method for austenitic stainless steel welds. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0047] The present invention will now be described in detail with reference to the accompanying drawings.

[0048] Reference Figure 1 and Figure 2 This invention provides a surface heat treatment method for austenitic stainless steel welds, comprising the following steps: A heating zone is provided on the surface of the weld, cooling zones are provided on both sides of the heating zone, and a temperature measuring zone is provided on the back side of the weld corresponding to the heating zone.

[0049] (1) Determine the heat treatment process parameters of the heating zone

[0050] The heat treatment process parameters of the heating zone are determined based on the material properties and weld size of the object to be heat treated, including the heat treatment termination temperature, the width of the heating zone, and the induction heating method.

[0051] In this step, the wall thickness of the heat-treated object is more than 10 mm, the heat treatment termination temperature is 1050-1080℃, the width of the heating zone is the weld and the weld extends 5-10 mm towards the base material; the induction heating is high-frequency induction heating with an induction heating frequency of 30-100 kHz.

[0052] (2) Determine the location of the cooling zone and the temperature of the temperature measurement zone through numerical simulation.

[0053] Based on the material properties, material structure parameters and heat treatment process parameters of the heat-treated object in step (1), an induction heating numerical simulation test is performed on the heat-treated object to obtain the time-temperature curve along the axial direction of the weld surface and the time-temperature curve of the back temperature measurement area of ​​the weld. The location of the cooling zone is determined based on the time-temperature curve of the weld surface. The temperature value of the back of the weld when the temperature of the weld surface reaches the heat treatment termination temperature in step (1) is determined based on the time-temperature curve of the heating zone of the weld surface and the time-temperature curve of the back temperature measurement area of ​​the weld. This temperature value is used as the heating termination temperature.

[0054] The specific steps of the numerical simulation experiment in this step are as follows:

[0055] Based on the structural dimensions and materials of the heat-treated object, a numerical simulation model is established, and an air domain model with a size 5 to 10 times that of the heat-treated object model is also established.

[0056] The numerical simulation model is meshed, and at least 5 boundary layers are divided in the thickness direction of the heating zone of the heat-treated object during meshing. At the same time, an infinite element domain is set at the edge of the air domain.

[0057] An induction heating device is applied to the numerical simulation model. When modeling the induction heating device numerically, only the coil structure is considered, and the coil is assigned corresponding parameters according to the current and frequency of the induction power supply of the induction heating device.

[0058] Numerical simulation was performed using the finite element method to obtain the time-temperature curves of the weld surface along its axial direction and the time-temperature curves of the temperature measurement area on the back of the weld.

[0059] In addition, in this step, when determining the location of the cooling zone based on the time-temperature curve of the weld surface, the area where the temperature on both sides of the weld stays within 600 to 650°C for more than one-third of the heating time is selected as the location of the cooling zone.

[0060] In addition, in this step, when determining the heating termination temperature based on the time-temperature curve of the weld surface heating zone and the time-temperature curve of the weld back temperature measurement zone, the temperature of the center point of the weld surface heating zone and the center point of the weld back temperature measurement zone shall be used as the standard.

[0061] (3) Arrange heating devices, cooling devices and temperature measuring devices.

[0062] (31) An electromagnetic induction heating device is arranged on the surface of the weld of the heat-treated object according to the width of the heating zone determined in step (1); the electromagnetic induction heating device maintains a certain gap with the surface of the weld of the heat-treated object through a vertically placed iron sheet or heat-resistant plate, the gap being 5 to 10 mm, and the electromagnetic induction heating device is as close as possible to the weld heating zone.

[0063] In this step, the electromagnetic induction heating device specifically uses air-cooled / water-cooled high-temperature resistant cables or copper pipes. The width of the electromagnetic induction heating device is equal to the width of the heating zone of the heat-treated object. If the minimum coverage area of ​​the electromagnetic induction heating device parallel to the longitudinal direction of the weld is greater than the width of the heating zone of the weld longitudinal direction of the heat-treated object, resulting in some heating devices exceeding the heat-treated object and causing no load, then a magnetic steel plate needs to be placed flat under the partially unloaded heating devices to prevent power loss caused by leakage magnetic field of the electromagnetic reaction heating device.

[0064] (32) According to the location of the cooling zone determined in step (2), a set of cooling devices are arranged in the cooling zones on both sides of the heating zone. Each set of cooling devices consists of three perforated copper pipes, with water as the cooling medium in the middle perforated copper pipe and air as the cooling medium in the other two perforated copper pipes.

[0065] In this step, when arranging the cooling device, the distance between the cooling device and the surface of the heat-treated object is kept at more than 10mm; and the three perforated copper pipes of the cooling device are all equipped with regulating valves for adjusting the flow rate of the cooling medium.

[0066] (33) Arrange thermocouples or infrared thermometers in the temperature measurement area on the back of the weld of the heat-treated object as temperature measurement devices, and obtain the time-temperature curve of the temperature measurement area on the back of the weld.

[0067] In this step, the temperature measuring device is a thermocouple or an infrared temperature measuring element; when the temperature measuring device is a thermocouple, the thermocouple is fixed to the temperature measuring area on the back of the weld by spot welding, and the thermocouple is preferably a K-type thermocouple; when the temperature measuring device is an infrared temperature measuring element, the infrared temperature measuring element is fixed at a position where the temperature measuring area on the back of the weld can be directly measured, ensuring that the temperature measuring point remains stationary during the temperature measurement process.

[0068] (4) Heat treatment implementation

[0069] The electromagnetic induction heating device heats the surface of the weld of the heat treatment object with a constant power. The heating stops when the temperature of the temperature measuring area on the back of the weld reaches the heating termination temperature determined in step (2). During the heating process, the open copper pipe with air as the cooling medium is opened intermittently. After the heating stops, the induction heating power is turned off, and the open copper pipe with water as the cooling medium or both water and air as the cooling medium is turned on to cool down. After the temperature of the temperature measuring area on the back of the weld reaches room temperature as measured by the temperature measuring device, the corresponding open copper pipe is turned off. In addition, if the surface temperature of the weld of the heat treatment object cannot be rapidly increased to the set heat treatment temperature at 600-700℃ / min due to the power or frequency limitation of the induction power, the open copper pipe with air as the cooling medium does not need to be opened intermittently during the heating process. After the heating is completed, the open copper pipe with water as the cooling medium is turned on to cool down.

[0070] (5) Remove the heating device, cooling device and temperature measuring device.

[0071] After the heat treatment is completed, the heating device, temperature measuring device and cooling device are removed, and the weld is subjected to non-destructive testing.

[0072] Example 1

[0073] A sample with a size of 100×200mm was cut from a 10mm thick 316L austenitic stainless steel welded plate produced by a steel mill, and the surface of the sample was heat-treated.

[0074] In this embodiment, the heat treatment termination temperature range is set to 1050-1080℃, the heating zone width is 20mm, the induction heating method is high-frequency induction heating, the output frequency of the induction heating power supply of the electromagnetic induction heating device is 30kHz, the output current is 70A, and it is equipped with a 24x current amplifier.

[0075] Because the distance between the electromagnetic induction heating device and the plate is small, the thermocouple cannot function properly due to the alternating electric field. Therefore, numerical simulation experiments of induction heating were conducted on the heat-treated object to obtain the time-temperature curve along the axial direction of the weld surface and the time-temperature curve of the temperature measuring area on the back side of the heated surface. Then, based on the time-temperature curve of the weld surface, the location of the cooling zone was determined. Specifically, the area where the temperature on both sides of the weld remains within the range of 600-650℃ for more than one-third of the heating time was selected as the location of the cooling zone. Furthermore, based on the time-temperature curve of the center of the heated zone on the weld surface and the time-temperature curve of the center of the temperature measuring area on the back side of the weld, the temperature value on the back side of the weld when the weld surface temperature reaches the set heat treatment termination temperature was determined, and this temperature value was used as the heating termination temperature. The time-temperature curve of the center of the heated zone on the weld surface is shown below. Figure 3 As shown, the time-temperature curve at the center of the corresponding weld back side temperature measurement zone is as follows: Figure 4 As shown in the figure, when the induction heating frequency is 30kHz, the temperature at the center of the weld surface heating zone reaches 1000℃ after approximately 150s and 1050℃ after approximately 162s. If a power supply with a higher induction heating frequency is used, the heating efficiency can be further improved. For example, when the induction heating frequency is 80kHz, the temperature at the center of the weld surface heating zone reaches 1050℃ after approximately 65s. This demonstrates high heating efficiency, further shortens the heating time, and allows the temperature to continue rising even without an insulation layer, as the heating time increases. Furthermore, from... Figure 3 and Figure 4As can be seen, when the temperature at the center of the heated zone on the weld surface reaches the set heat treatment termination temperature of 1050–1080℃, the temperature at the center of the corresponding temperature measurement zone on the back side of the weld is 965℃. This temperature value is taken as the actual heating termination temperature during the heating process. Furthermore, during the numerical simulation, the time-temperature curve along the axial direction of the weld surface of the heat-treated object is also obtained to determine the location of the cooling zone. Specifically, the area where the temperature on both sides of the heated zone remains within the 600–650℃ range for more than one-third of the heating time is selected as the location for the cooling zone. Figure 5 As shown, the cooling zone was positioned 20–30 mm from the heating center. Additionally, the temperature change over time at a location 70 mm from the center of the heating zone on the sample surface is shown below. Figure 6 As shown, from Figure 6 As can be seen, due to the setting of the cooling zone, the temperature rise in other areas far from the weld and the cooling zone is not significant.

[0076] Based on the determined heating termination temperature of the center of the back-side temperature measuring zone of the weld and the arrangement of the cooling zone, the plate sample is heat-treated. A heating device, a cooling device, and a temperature measuring device are arranged on the plate sample. The heating device uses a single copper tube inductor, with a 25mm copper square tube placed flat on the part to be heated, with a 5mm gap between it and the plate sample. The internal cooling medium is water. A cooling device consisting of three perforated copper tubes is arranged in the cooling zone on both sides of the heating zone, and a thermocouple is arranged in the temperature measuring zone on the back side of the weld. After the arrangement is completed, the plate sample is heat-treated. Heating is stopped when the temperature of the temperature measuring zone on the back side of the weld reaches the determined heating termination temperature. During the heating process, the perforated copper tube with air as the cooling medium is intermittently opened. After heating is stopped, the induction heating power supply is turned off, and the perforated copper tube with water as the cooling medium or with both water and air as the cooling medium is opened for cooling. After the temperature of the back-side temperature measuring zone of the weld measured by the temperature measuring device reaches room temperature, the corresponding perforated copper tube is closed. After the heat treatment is completed, the heating device, temperature measuring device, and cooling device are removed.

[0077] In this embodiment, during the heat treatment of austenitic stainless steel welds, the induction heating device is brought as close as possible to the workpiece to be heat-treated, ensuring that the surface temperature of the workpiece reaches the required heat treatment temperature of 1050–1080°C without the need for an insulation layer. Furthermore, by installing cooling devices on both sides of the weld, the residence time of the base material in the sensitization temperature zone is reduced, preventing Cr from being absorbed. 23 Deterioration caused by the precipitation of carbides such as C6.

[0078] Comparative Example 1

[0079] A sample measuring 100×200mm was cut from a 10mm thick 316L austenitic stainless steel welded plate produced by a steel mill and subjected to overall heat treatment.

[0080] The electromagnetic induction heating device for overall heat treatment uses a coil, which is made of copper tubing with an outer diameter of 10mm and water as the internal cooling medium. The output frequency of the induction heating power supply is 10kHz and the output current is 200A. The distance between the induction heating coil and the plate sample is 40mm. When the coil is used to wrap around the plate sample, refractory bricks are placed under the plate to separate the coil from the plate sample.

[0081] Temperature was collected at the center of the plate using a thermocouple spot weld. In this example, the coil was far from the heat-treated sample, and the thermocouple was less affected by the alternating current, thus allowing direct acquisition of the sample's surface temperature. The temperature change over time at the center of the weld surface of the plate during heating is shown below. Figure 7 As shown, the temperature at the measuring point reached 1000℃ after about 250 seconds of heating. After that, due to the lack of an insulation layer and the large distance between the induction heating coil and the sample, the heat exchange between the high-temperature sample and the air caused the temperature of the sample to remain at 1000℃ and not rise further, failing to reach the required temperature range of 1050-1080℃ as specified in the process.

[0082] Meanwhile, using the numerical simulation method of Example 1, numerical simulation was performed according to the structural parameter settings of Comparative Example 1. The temperature change curve of the center part of the weld surface obtained by the numerical simulation was basically consistent with the temperature change curve measured by the thermocouple. It was heated to about 1000℃ in about 230s and basically stabilized. It was still difficult to reach 1050-1080℃ with continued heating.

[0083] It should be noted that any parts not mentioned in this invention can be achieved by using or referencing existing technologies.

[0084] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

[0085] It should be noted that any parts not mentioned in this invention can be achieved by using or referencing existing technologies.

[0086] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A surface heat treatment method for austenitic stainless steel welds, characterized in that, A heating zone is set on the surface of the weld, cooling zones are set on both sides of the heating zone, and a temperature measuring zone is set on the back of the weld corresponding to the heating zone, including the following steps: (1) Determine the heat treatment process parameters of the heating zone The heat treatment process parameters of the heating zone are determined based on the material properties and weld size of the object to be heat treated, including the heat treatment termination temperature, the width of the heating zone, and the induction heating method. (2) Determine the location of the cooling zone and the temperature of the temperature measurement zone through numerical simulation. Based on the material properties, material structure parameters and heat treatment process parameters of the heat-treated object in step (1), an induction heating numerical simulation test is performed on the heat-treated object to obtain the time-temperature curve of the weld surface along its axial direction and the time-temperature curve of the temperature measurement area on the back of the weld. The location of the cooling zone is determined based on the time-temperature curve of the weld surface along its axial direction. The temperature value of the back of the weld when the temperature of the weld surface reaches the heat treatment termination temperature in step (1) is determined based on the time-temperature curve of the heating zone of the weld surface and the time-temperature curve of the temperature measurement area on the back of the weld. This temperature value is used as the heating termination temperature. (3) Arrange heating devices, cooling devices and temperature measuring devices. (31) Arrange an electromagnetic induction heating device on the surface of the weld of the heat-treated object according to the width of the heating zone determined in step (1); (32) According to the location of the cooling zone determined in step (2), a set of cooling devices are arranged in the cooling zones on both sides of the heating zone. Each set of cooling devices consists of three perforated copper pipes, with water as the cooling medium in the middle perforated copper pipe and air as the cooling medium in the other two perforated copper pipes. (33) Arrange thermocouples or infrared thermometers in the temperature measurement area on the back of the weld of the heat-treated object as temperature measurement devices, and obtain the time-temperature curve of the temperature measurement area on the back of the weld. (4) Heat treatment implementation The electromagnetic induction heating device heats the surface of the weld of the heat treatment object with constant power. The heating stops when the temperature of the temperature measuring area on the back of the weld reaches the heating termination temperature determined in step (2). During the heating process, the open copper pipe with air as the cooling medium is opened intermittently. After the heating stops, the induction heating power is turned off and the open copper pipe with water as the cooling medium or with both water and air as the cooling medium is turned on to cool down. After the temperature of the temperature measuring area on the back of the weld measured by the temperature measuring device reaches room temperature, the corresponding open copper pipe is closed. (5) Remove the heating device, cooling device and temperature measuring device. After the heat treatment is completed, the heating device, temperature measuring device and cooling device are removed, and the weld is subjected to non-destructive testing. In step (2), when determining the heating termination temperature based on the time-temperature curve of the weld surface heating zone and the time-temperature curve of the weld back temperature measurement zone, the temperature of the center point of the weld surface heating zone and the center point of the weld back temperature measurement zone shall be used as the standard.

2. The surface heat treatment method for austenitic stainless steel welds according to claim 1, characterized in that, In step (1), the wall thickness of the heat-treated object is more than 10 mm, the heat treatment termination temperature is 1050~1080℃, and the width of the heating zone is the weld and the weld extends 5~10 mm towards the base material.

3. The surface heat treatment method for austenitic stainless steel welds according to claim 1, characterized in that, In step (1), the induction heating is high-frequency induction heating.

4. The surface heat treatment method for austenitic stainless steel welds according to claim 3, characterized in that, The induction heating frequency is 30~100kHz.

5. The surface heat treatment method for austenitic stainless steel welds according to claim 1, characterized in that, In step (2), when determining the location of the cooling zone based on the time-temperature curve along the axial direction of the weld surface, the area where the temperature on both sides of the weld stays within 600~650℃ for more than one-third of the heating time is selected as the location of the cooling zone.

6. The surface heat treatment method for austenitic stainless steel welds according to claim 1, characterized in that, In step (31), the width of the electromagnetic induction heating device is equal to the width of the heating zone of the heat-treated object.

7. The surface heat treatment method for austenitic stainless steel welds according to claim 1, characterized in that, In step (32), when arranging the cooling device, the distance between the cooling device and the surface of the heat-treated object is kept at more than 10 mm; and the three perforated copper pipes of the cooling device are all equipped with regulating valves for adjusting the flow rate of the cooling medium.

8. The surface heat treatment method for austenitic stainless steel welds according to claim 1, characterized in that, In step (33), the temperature measuring device is a thermocouple or an infrared temperature measuring element. When the temperature measuring device is a thermocouple, the thermocouple is fixed to the temperature measuring area on the back of the weld by spot welding. When the temperature measuring device is an infrared temperature measuring element, the infrared temperature measuring element is fixed at the position where the temperature measuring area on the back of the weld can be directly measured.

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